Earlier this month, we reported that Microsoft would be launching a new ad-supported music streaming service called Xbox Music alongside Windows 8. Microsoft officially announced today that Xbox Music would be available for free streaming on Windows 8 and Windows RT tablets.

Microsoft says that this is the first all-in-one music service allowing users to stream custom playlists at no cost, subscribe to all the music user wants, and provide the ability to download tracks to own.

Microsoft says that Xbox Music has over 30 million songs and will begin rolling out around the world today on the Xbox 360 and later this month for Windows 8 and Windows RT PCs and tablets. The service will also be available for Windows Phone 8 when it launches. In case you were wondering, Windows Phone 7.x devices won’t get access to the service.

“The launch of Xbox Music is a milestone in simplifying digital music on every type of device and on a global scale,” said Don Mattrick, president of the Interactive Entertainment Business at Microsoft. “We’re breaking down the walls that fracture your music experiences today to ensure that music is better and integrated across the screens that you care about most — your tablet, PC, phone and TV.”

The free service for Windows 8 and RT computers will allow users to access songs and stream them instantly. The free service allows for the creation of an unlimited number of playlists as well.

Users who want access to music offline will be able to get ad-free unlimited playback for $9.99 per month. Paying for the service also unlocks access to tens of thousands of music videos on the Xbox 360.

Microsoft says that in the coming year, cloud storage will be available, allowing users to add music to their own Xbox Music cloud catalog. That cloud catalog will be able to include music purchase outside of Xbox Music.